Mold pattern

ABSTRACT

A permanent type non-expendable pattern for making refractory molds in which portions of the pattern are retractable from a projected position in which they are disposed in the cavity to be filled with the refractory molding material and a retracted position in clearance relationship relative to the refractory mold material, enabling an extraction of the pattern from the refractory mold produced. The retractable pattern sections, when in the projected position, are locked in accurate registration with the frame of the pattern, but upon initiation of retraction, are unlocked so as to enable pivoting movement of the sections, whereby they can be withdrawn from the mold cavities formed without damaging the mold surfaces.

[ 1 June 27, 1972- MOLD PATTERN [72] Inventors: Ronald B. Buck, Jr.,Farmington; Ted

Zbikowski, Southfield, both of Mich.

[73-] Assignee: Eaton Corporation [22] Filedz March 23, 1970 [21]Appl.No.: 21,758

[52] US. Cl. ..l64/247, 18/DIG. 58, 249/64, 249/63, 249/59, 164/215 [51Int. Cl. ..B22c 7/00, B22c 9/22 [58] Field of Search ..164/247, 248,215,216,133, 164/333, 332, 334, 240; 249/63, 64, 59, 84, 90, 60; l8/D1G.58

[56] References Cited UNITED STATES PATENTS 2,611,161 9/1952 Paul et a1...164/215 2,887,744 5/1959 l-lalliday..... ....l64/247 207,656 9/1878Haines ..249/64 209,811 11/1878 Huntley ..l64/247 125,186 4/1872 Finch....164/248 2,151,131 3/1939 McWane ..249/63 1,551,193 8/1925 Flammanget al. ...249/63 X 416,333 12/1889 Hogan ..164/248 3,313,875 4/1967Magerle ..18/36 2,745,353 5/1956 Syrovy... ....l64/333 X 2,363,80811/1944 Sayre ..18/D1G. 58

FOREIGN PATENTS OR APPLICATIONS 482,142 9/1929 Germany ..l64/247 423,2492/1911 France 164/247 Primary Examiner-J. Spencer Overholser AssistantExaminer-V. K. Rising Attorney-Harness, Dickey & Pierce [57] ABSTRACT Apermanent type non-expendable pattern for making refractory molds inwhich portions of the pattern are retractable from a projected positionin which they are disposed in the cavity to be filled with therefractory molding material and a retracted position in clearancerelationship relative to the refractory mold material, enabling anextraction of the pattern from the refractory mold produced. Theretractable pattern sections, when in the projected position, are lockedin accurate registration with the frame of the pattern, but uponinitiation of retraction, are unlocked so as to enable pivoting movementof the sections, whereby they can be withdrawn from the mold cavitiesformed without damaging the mold surfaces.

10 Claims, 7 Drawing Figures j 44 //A //i //4 PATENTEUJUHZ? I972 3,672.435

SHEET 1 OF 3 INVENTORS.

PATEHIED JUH 2 7 I272 SHEU 3 or 3 INVENTORi MOLD PATTERN BACKGROUND OFTHE INVENTION The use of refractory-type molds composed of silica orceramic particles bonded by organic or inorganic binding agents is inwidespread commercial use for making precisiontype castings, requiringonly minimal final machining operations. Typical of such techniques isthe so-called lost wax or investment casting process which employsexpendable patterns that are composed of waxes or plastic materials. Theexpendable patterns are conventionally formed in metal dies and areassembled to form a composite pattern of the desired configuration. Theresultant expendable patterns are thereafter employed for making therefractory mold in which the embedded pattern corresponds to the moldcavity which subsequently is to be filled with molten metal. The removalof the expendable pattern after the refractory mold has solidified orcured is achieved by the application of heat, effecting a melting,vaporization or thermal degradation of the pattern, leaving a cavity ofthe desired configuration.

A continuing problem associated with such expendable patterns is theirsusceptibility to distortion and breakage during handling and forming ofrefractory molds, which in turn results in mold cavities which are ofinaccurate size and configuration. In addition, in the formation ofexpendable patterns of relatively complicated shape, a plurality ofindividual sections are conventionally used that must be manuallyassembled and accurately secured together. This practice constitutes acostly and time consuming operation.

The increasing use of gas turbines as a source of power has placedrenewed emphasis on the need for economical manufacturing processes formaking turbine wheels and similar components that are of accuratedimensions and balance as is required due to the high speed andcentrifugal stresses to which such parts are subjected during use. Ithas been necessary in the past to form such turbines wheels byindividually machining and assembling each blade or bucket to a hubwhich constitutes a costly manufacturing operation and has detractedfrom a more widespreaduse of such engines. Alternatively. investmentcasting processes employing expendable patterns have been used orproposed for use, but the complexity of the part and the fragile natureof the patternsproduced has resulted in relatively high costs infabricating the patterns, as well as a relatively high scrap rate due toinadvertent warpage or distortion of the patterns during the formationof the refractory molds.

The foregoing and other problems and disadvantages of investment-typecasting processes for making turbine wheels and like components ofcomplicated configuration are overcome in accordance with the permanentnon-expendable pattern of the present invention which is of highstrength and extremely accurate final dimensions, enabling its repeatedreuse for making successive refractory molds, each havingaccurately-sized and shaped mold cavities therein.

SUMMARY OF THE INVENTION The benefits and advantages of the presentinvention are achieved by a non-expendable pattern suitable for makingrefractory-type molds which is composed of a high strength,abrasion-resistant material and consists of a frame of which a portionthereof is provided with a pattern surface which is of a preselectedconfiguration and which is formed with one or more aperturestherethrough that are disposed in communication with the patternsurface. A pattern section is movably and guidably mounted on the frameand is disposed in each of the apertures thereof for movement between aprojected position in which the section projects outwardly of thepattern surface and a retracted position in which the section iswithdrawn inwardly of the pattern surface. Coacting means are providedon the frame and each section for fixedly positioning the section inprecise registration relative to the pattern surface when the section isin the projected position and for disengaging the section during itsretraction, enabling movement of the section so as to permit itswithdrawal from the mold cavity formed without damaging or otherwisedisturbing the surface of the mold cavity.

Additional benefits and advantages of the present invention will becomeapparent upon a reading of the description of the preferred embodimentstaken in conjunction with the accom' panying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic elevation viewpartly in section illustrating a typical assembly of the non-expendablepattern and molding components for making a refractory-type mold;

FIG. 2 is a plan view of an individual turbine blade pattern assemblycomprising a movable section of the permanent pattern;

FIG. 3 is an end view of the individual blade pattern shown in FIG. 2 asviewed from the base end of the turbine blade;

FIG. 4 is an end view of the individual blade pattern shown in FIG. 2,as viewed from the tip end of the turbine blade;

FIG. 5 is a fragmentary vertical transverse sectional view through thenon-expendable pattern with the turbine blades disposed in a projectedposition;

FIG. 6 is a fragmentary plan view with portions broken away for clarityof the non-expendable pattern shown in FIG. 5; and

FIG. 7 is a vertical sectional view taken through the linkage connectingthe individual blade patterns as shown in FIG. 5, and takensubstantially along the line 77 thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now in detail to thedrawings and as is best illustrated in FIG. 1, a typical assembly isshown for making refractory-type molds for casting turbine wheelscomprising a base 10 on which a permanent non-expendable pattern 12 isaccurately positioned. The base 10 is formed with a central aper ture 14extending inwardly of the upper surface thereof into which an aligningpin 16 of the pattern 12 is adapted to be slidably disposed formaintaining these two components in proper registration. An annularback-up mold 18 is positioned on the base and encircles the periphery ofthe pattern 12 defining therebetween an annular mold cavity 20, intowhich retractable pattern sections, such as turbine blades 22, project.A suitable particulated molding material 23, containing a bonding agent,is introduced into the mold cavity 20 by means of an annular tubularmember 24, removably disposed on the upper surfaces of the back-up mold18 and the pattern 12. After a setting of the molding material 23, inwhich it attains sufficient strength to retain dimensional accuracy, theblades 22 are withdrawn inwardly of the pattern 12 and the entirepattern is lifted upwardly, leaving a composite mold consisting of theback-up mold 18 having a lining around its inner surface incorporating aplurality of circumferentially spaced cavities which conform to theconfiguration of the turbine blades 22. It will be noted that theperiphery of the pattern is of a configuration to provide satisfactorydraft angles so as to enable upward withdrawal of the pattern from themold after the blades have been retracted. The resultant composite moldis thereafter assembled with appropriate cores for receiving the moltenmetal to form a turbine wheel of the requisite configuration.

The details of the construction of the permanent non-expendable pattern12 will now be described with specific reference to FIGS. 2-7 of thedrawings. The movable or retractable mold sections comprise a pluralityof individual blade assemblies 26, as best seen in FIGS. 2-4, each ofwhich comprises a blade portion 28 and a supporting pin 30 integrallyconnected thereto. Each blade assembly may be composed of ahigh-strength injection molded plastic material such as polystyrene, forexample, or of a suitable metal or metal alloy. The supporting pin 30 isof a cylindrical configuration and is provided with a smooth surfacefinish. The blade portion 28 is composed of a root section 32, which isprovided with an air foil shaped cross section. The root section extendsfrom a rear surface 34 to an arcuate face surface 36, from which a blade38 projects. The root section 32, as best seen in FIGS. 2 and 4, isformed with a tapered peripheral surface 40 being of progressivelydecreasing cross sectional area on moving from the rear surface 34 tothe face surface 36. In addition, a tab 42 is integrally formed on theroot section 32, which serves as a stop for establishing the outermosttravel of the blade assembly when it attains the fully projectedposition.

The blade 38, which is integrally formed with the root section 32, isprovided with an air foil shaped cross section and is of a variablepitch on moving from the face surface of the root section to the tip 44of the blade. The variation in the pitch of the blade being greatest atthe tip 44 forms two warped surfaces having a gradual twist or helicalconfiguration. The thickness of the blade 38 itself increases on movingfrom the tip 44 toward the root section 32.

It will be apparent from the configuration of the blade 38 that thetwist of the blade, due to the variation in pitch thereof, prevents anaxial withdrawal of the blade from a mold cavity as defined by moldingmaterial disposed therearound without incurring distortion and damage tothe mold cavity surfaces. In accordance with the permanentnon-expendable pattern of the present invention, each of the bladeassemblies undergoes a rotation about the axis of its supporting pin 30during retraction thereof, whereby the surfaces of the blade follow thesurface contour of the molding cavity formed, providing a resultant moldhaving accurate and smooth surfaces for receiving the molten metal to becast.

A typical embodiment of the supporting arrangement and retractingmechanism for each of the blade assemblies will now be described withparticular reference to FIGS. -7 of the drawings. The framework of thepattern comprises a central shaft 46, which is formed with a radiallyextending flange 48 disposed intermediate the ends thereof. The radialflange 48 is provided with an integrally formed annular flange 50 alongits lower peripheral surface which is provided with a first plurality ofsubstantially radially extending guide bores 52 in which the supportingpins 30 of the blade assemblies 26 are slidably disposed. The lowerportion of the shaft 46 is ofa preselected diameter so as to serve asthe aligning pin 16, as previously described in connection with FIG. 1,and is adapted to be removably received in the aligning bore 14extending centrally through the base for accurately positioning thepattern 12 on the mold base.

The shaft 46 is formed with a centrally extending bore 54 which isprovided with a recess 56 at the lower end thereof and a counterbore 58of enlarged diameter extending inwardly and concentrically of the bore54 at the upper end thereof, as best seen in FIG. 5. A stepped pin 60 isdisposed with its lower shank in the bore 54 and with its shoulder 62seated on a shoulder 63 formed at the intersection of the bore 54 andcounterbore 58. The stepped pin is secured in the bore 54 by means of asocket head cap screw 64 which is disposed in threaded engagement in thelower end thereof with its head portion positioned within the recess 56.The upper peripheral portion of the shaft 46 disposed upwardly of theradially extending flange 48 is of a uniform and smooth circular crosssection and a flanged sleeve 66 is disposed in sliding encirclingrelationship therearound. The upper portion of the flanged sleeve 66 isformed with exterior threads 68 on which a cylindrical cap 70 isthreadably engaged and retained in appropriate axial disposition thereonby means of a lock nut 72. The end of the cap 70 is formed with acentral threaded bore 74, through which the shank of a locking screw 76is adapted to extend and to be disposed in threaded engagement within athreaded bore 78, extending axially and inwardly of the upper end of thestepped pin 60.

The locking screw 76 is adapted to clamp the cap and the flanged sleeve66 in the position as shown in solid lines in FIG. 5, which correspondsto the position in which the blade assemblies are disposed in theprojected position. Movement of the flanged sleeve and cap upwardly fromthe position as shown in solid lines in FIG. 5 to effect a retraction ofthe blade assemblies is achieved in response to the removal of thelocking screw 76 which is assisted by a coil spring 80 disposed inencircling relationship around the upper end of the stepped pin 60having its ends seated, respectively, against the underside of the endwall of the cap 70 and the shoulder 63 formed between the bore 54 andcounterbore 58.

To further facilitate upward movement of the flanged sleeve and capduring a retraction of the blade assemblies, an extracting screw (notshown) can be inserted in threaded engagement in the threaded bore 74provided in the end wall of the cap and turning the extractor screwinwardly until its shank end is disposed in bearing engagement against aconcave seat 82 formed in the upper end of the stepped pin 60. Rotationof the extractor screw effects an axial extracting movement of the capand flanged sleeve, effecting a retraction of the blade assembliesthrough a linkage arrangement as hereinafter described.

Each blade assembly 26 is individually retracted by means of a pivotallyconnected link arm 84 having its inner end pivotally secured about asteel ball 86 secured within a spherical opening in a radially extendingslot 88 formed in the periphery of the flanged sleeve 66 and itsopposite outer end pivotally secured to a guide yoke 90. The guide yoke90, as best seen in FIGS. 5 and 7, is formed with a slot 92 through itsupper end for receiving the end of the link arm which is pivotallysecured therein by means of a pivot pin 94. The guide yoke is securelyfastened to a guide pin 96, which is slidably disposed in a secondseries of guide bores 98, which extend in a substantially radialdirection through the upper portion of the annular flange 50. The lowerportion of the guide yoke 90, as shown in FIG. 7, is formed with ahookshaped portion that is adapted to partially overlie the periphery ofthe supporting pin 30 of a blade assembly.

The rearward surface of the hook-shaped portion 100 is disposed inbearing relationship against a collar 102 secured such as by means ofset screws 104 to the supporting pin 30 of each blade assembly. Theforward face of the hook-shaped portion 100 is disposed in bearingcontact against a spring washer 106 overlying the rear surface 34 of theroot section of a blade assembly.

In accordance with this arrangement, upward movement of the flangedsleeve 66 and the cap 70 affixed thereto from the position as shown insolid lines in FIG. 5 effects an angular pivoting movement of each ofthe link arms 84 from the position as shown in solid lines to thepositions as shown in phantom, effecting thereby a retraction of each ofthe blade assemblies wherein the tips of the blades are withdrawninwardly of the pattern framework. Projecting movement of the bladeassemblies is achieved by a reversal of the foregoing steps in which theflanged sleeve 66 is moved downwardly wherein the link arms assume thepositions as shown in solid lines in FIG. 5, whereby the blades areretained in the fully projected position in response to the outwardforce exerted by the hookshaped portions 100 of the guide yokespositioned against the spring washers 106.

As will be noted, the peripheral portion of the non-expendable patternis defined by an annular rim 108 including a radial flange 110 which issecurely fastened, such as by means of socket head screws 112, to theunderside of the annular flange 50, as shown in FIG. 5. The upwardly andoutwardly tapered circular flange 114 of the annular rim 108 is formedwith a plurality of apertures 116 at circumferentially spaced intervalstherealong, which are of a configuration corresponding to the crosssectional configuration of the root section 32 of the blade assemblies.The apertures 116 have correspondingly inwardly tapered surfaces forreceiving the tapered peripheral surfaces 40 of each blade portion,effecting appropriate registration therebetween, wherein the blade 38 isdisposed at the proper pitch. The stop tab 42 on the root section 32 isadapted to engage and overlie the rear surface of the circular flange114, assuring that the blade portion is in the appropriate projectedposition.

The coaction between the inwardly tapered surfaces of the apertures 116and the tapered peripheral surface 40 of each blade assembly serves tolock each blade when it attains the fully projected position inappropriate angular disposition relative to the pattern framework. Uponthe initiation of retraction of the blade assemblies, a disengagementoccurs between the tapered peripheral surface 40 of the blade portionsand the conforming surfaces of the apertures 116, whereby the bladeassemblies are free to rotate about the axes of the supporting pins 30,enabling rotation of the blade to conform with the helical configurationof the mold cavity formed. As will be noted in FIG. 6, the axes of thesupporting pins are angularly offset from a true radial position suchthat the blades during retraction are withdrawn from the mold cavitieswithout interference with the mold surfaces. The particular angle ofretraction can be varied in accordance with the specific geometry of theturbine blades.

As shown in FIG. 5, the face surface 36 of the root section 32 of theblade assembly is contoured so as to conform exactly with theconfiguration of the outer surface of the circular flange 1 14, whichitself is contoured, adjacent to the apertures 116 to form a patternsurface against which the molding material is adapted to be disposed.The exterior or pattern sur' face 1 18 of the circular flange 1 14, theupper surface of an annular mold ring 120, the inner surface of anannular back-up mold ring 122 and the lower surface of an upper moldring 124, which is secured by means of screws 126 to the upper edge ofthe circular flange 114, define therebetween an annular mold cavity 128,into which the blades 38 project. A suitable molding material is pouredinto the mold cavity 128 such as by means of a series of angular chutes130 formed in the upper mold ring 124. The close tolerance between thetapered peripheral surface 40 of the blade assemblies and the taperedapertures 1 16 form a seal, preventing leakage of any molding materialinwardly of the pattern assembly.

While the description of the present invention is made with respect to apermanent pattern for making turbine wheels of a type having a centralhub from which a plurality of blades ex tend in a substantially radialdirection, it will be appreciated that the present invention is alsoapplicable for forming stators and like components including an annularrim having a plurality of blades projecting radially inwardly therefrom.The principle of operation of the permanent non-expendable pattern asherein described is also applicable for forming molds of any one of avariety of types and compositions where precision castings are requiredand wherein selected sections of the pattern must be retracted in orderto enable separation of the mold and pattern.

We claim:

1. A pattern for producing a mold having a bladelike cavity of twistedconfiguration, said pattern comprising: a frame defining a mold cavity;a pattern section having a twisted configuration; guide means connectedto said pattern section and in sliding engagement with said frame, saidguide means being adapted to move said pattern section a given distanceinto said mold cavity and to move said pattern section out of said moldcavity, said pattern section being free to rotate relative to said guidemeans; and locking means to retain said pattern section in apredetermined position relative to said mold cavity when said patternsection is at said given distance into said mold cavity.

2. The pattern as defined in claim 1, wherein said mold cavity is of acircular configuration having a central axis, said frame includes aplurality of apertures communicating with said mold cavity and disposedat circumferentially spaced intervals along said circular configurationand a pattern section is adapted to be moved through each aperture intoand out of said mold cavity.

3. The pattern as defined in claim 1, wherein said locking meanscomprises a tapered surface against which a conforming surface on saidpattern section is adapted to be disposed in bearing relationship whensaid pattern section is at said given distance into said mold cavit 4.The pattern as defined in claim 1, wherein said pattern section includesstop means adapted to coact with said frame for limiting the travel ofsaid pattern section at said given distance into said mold cavity.

5. The pattern as defined in claim 2, including linkage means connectedto each pattern section to effect movement of all of the patternsections in unison into and out of said mold cavity.

6. The pattern as defined in claim 6, including means connected to saidlinkage means for retaining said pattern sections at said given distanceinto said mold cavity.

7. The pattern as defined in claim 2 wherein: a shaft extends axiallythrough said central axis; a cap is adapted to be slid axially alongsaid shaft; a link arm connects each of said pattern sections to saidcap; and said guide means are movable normal to said shaft.

8. The pattern as defined in claim 7 wherein: said frame includes aplurality of passages extending in a direction normal to said shaft; andsaid guide means includes a guide pin slideably engaged in one of saidpassages and rigidly secured at one end to a guide yoke, said guide yokebeing pivotally connected to one of said link arms, said guide meansfurther includes a pin support slideably engaged in another of saidpassages and supported by said guide yoke, said pin support beingadapted to rotate relative to said guide yoke and being connected tosaid pattern section.

9. The pattern as defined in claim 8 wherein resilient means isinterposed between said guide yoke and said pattern section to exert aforce on said pattern section to retain said pattern section in a givenposition.

10. The pattern as defined in claim 7 wherein said cap includes aplurality of radially extending slots, a ball is secured in each of saidslots and one end of a link arm is pivotally secured about each of saidballs.

1. A pattern for producing a mold having a bladelike cavity of twistedconfiguration, said pattern comprising: a frame defining a mold cavity;a pattern section having a twisted configuration; guide means connectedto said pattern section and in sliding engagement with said frame, saidguide means being adapted to move said pattern section a given distanceinto said mold cavity and to move said pattern section out of said moldcavity, said pattern section being free to rotate relative to said guidemeans; and locking means to retain said pattern section in apredetermined position relative to said mold cavity when said patternsection is at said given distance into said mold cavity.
 2. The patternas defined in claim 1, wherein said mold cavity is of a circularconfiguration having a central axis, said frame includes a plurality ofapertures communicating with said mold cavity and disposed atcircumferentially spaced intervals along said circular configuration anda pattern section is adapted to be moved through each aperture into andout of said mold cavity.
 3. The pattern as defined in claim 1, whereinsaid locking means comprises a tapered surface against which aconforming surface on said pattern section is adapted to be disposed inbearing relationship when said pattern section is at said given distanceinto said mold cavity.
 4. The pattern as defined in claim 1, whereinsaid pattern section includes stop means adapted to coact with saidframe for limiting the travel of said pattern section at said givendistance into said mold cavity.
 5. The pattern as defined in claim 2,including linkage means connected to each pattern section to effectmovement of all of the pattern sections in unison into and out of saidmold cavity.
 6. The pattern as defined in claim 6, including meansconnected to said linkage means for retaining said pattern sections atsaid given distance into said mold cavity.
 7. The pattern as defined inclaim 2 wherein: a shaft extends axially through said central axis; acap is adapted to be slid axially along said shaft; a link arm connectseach of said pattern sections to said cap; and said guide means aremovable normal to said shaft.
 8. The pattern as defined in claim 7wherein: said frame includes a plurality of passages extending in adirection normal to said shaft; and said guide means includes a guidepin slideably engaged in one of said passages and rigidly secured at oneend to a guide yoke, said guide yoke being pivotally connected to one ofsaid link arms, said guide means further includes a pin supportslideably engaged in another of said passages and supported by saidguide yoke, said pin support being adapted to rotate relative to saidguide yoke and being connected to said pattern section.
 9. The patternas defined in claim 8 wherein resilient means is interposed bEtween saidguide yoke and said pattern section to exert a force on said patternsection to retain said pattern section in a given position.
 10. Thepattern as defined in claim 7 wherein said cap includes a plurality ofradially extending slots, a ball is secured in each of said slots andone end of a link arm is pivotally secured about each of said balls.